The present embodiments relate to ultrasound transducers, such as capacitive membrane ultrasound transducers (CMUTs) for medical diagnostic imaging. For a CMUT, microelectromechanical processes form an array of elements, such as a one or two-dimensional array of elements. Each element a plurality of cells or membranes with associated electrodes separated by includes a gap or void. Flexing of the membranes in response to acoustic energy generates an electrical signal. Applying an electrical signal across the electrodes similarly causes the membrane to flex, producing acoustic energy. To provide desired response, a bias voltage is also applied across the electrodes.
An insulating layer, such as silicon dioxide, covers or is adjacent one or each of the electrodes. As the CMUT is used, electrical charge may migrate across the insulating layer. The charge is maintained as static or surface charge. Accumulation of the surface charge may deteriorate the CMUT response.